Did you ever wonder how humans pick their partners? What parameters do we pay attention to when deciding who to mate with? Surely physical attraction plays a role, but is there anything else influencing this choice? Sexual selection plays an important role in the development of relationships.
- We will review the topic of human reproductive behaviour in psychology.
- First, we will explore the types of sexual selection.
- Throughout our explanation, we will provide sexual selection examples to help illustrate our points.
- Moving on from this, we will discuss the relationship between sexual selection and human reproductive behaviour.
- Finally, we will evaluate sexual selection, discussing the differences between sexual selection and human reproductive behaviour.
Fig. 1 - Sexual selection is an important aspect of relationship formation.
Human Reproductive Behaviour: Psychology
Sexual selection refers to the evolutionary explanation describing why humans prefer some partners over others. Sexual selection is deeply rooted in the evolutionary approach and, therefore, explains sexual selection in terms of survival and reproductive success.
In theory, those who exhibit certain characteristics within a population, which allows them to better find a partner to reproduce with, have a reproductive advantage over others.
Being physically attractive, for instance, increases the chances of finding a partner.
What traits are deemed desirable varies across cultures and societies. Due to the increased chances of finding a partner, these features have an increased chance of being passed down to children.
They become more common as generations pass.
For example, the waist-to-hip ratio in women is linked to chances of reproducing (fertility). Because of this, partners may prefer a particular waist-to-hip ratio to increase the chances of coupling with a women with higher fertility. We will discuss more on this later.
In line with the sexual selection definition, human reproductive behaviour is part of adaption, and therefore, individuals look for certain characteristics in their potential partners.
Types of Sexual Selection
The types of sexual selection emerge based on the strategies that women and men engage in regarding sexual selection. There are two types of sexual selection: inter-sexual selection and intra-sexual selection.
Inter-sexual selection refers to the competing nature males use to gain the attention of female partners. The female partner then chooses who they would like to mate with based on certain traits and preferences.
We can see inter-sexual attraction in some animal species.
Male birds, for instance, often have colourful feathers and perform dances to attract female attention.
Now, let's explore intra-sexual selection.
Intra-sexual selection refers to when males compete for a female of the same species, and the winner claims the right to mate with the female. Oftentimes, competing takes the form of aggression.
Intra-sexual selection may also explain physical differences between men and women. Some theories postulate that men are generally stronger and bigger as they need to maintain evolutionarily desirable characteristics to be selected by women (if men were bigger and stronger, they are more likely to survive and provide).
On the other hand, women choose mates to protect them and therefore do not need to have such traits to enable them to survive or reproduce. Instead, they develop traits desirable to the opposite sex.
Fig. 2 - Women and men develop differently according to their needs.
In 1989, psychologist David Buss surveyed the sexual selection and reproductive behaviour of over 10,000 adults' in 33 countries.
- He found that females placed more importance on resource-related characteristics such as ambition, high intelligence, and good financial prospects.
- In contrast, men preferred younger partners and placed more value on attractiveness and modesty, values that reflected a woman's ability to reproduce.
This shows the idea of anisogamy influences mate choice as men focus more on reproduction as they can reproduce more, whereas women seek to invest in a mate as they have a finite amount of time and reproductive cells to reproduce.
Similarly, Clark and Hatfield (1989) investigated differences between male and female reproductive behaviour on university campuses.
- They asked male and female students to approach the opposite sex and ask various questions, including propositions such as 'Will you go to bed with me tonight?'.
- They found that whilst the vast majority of men agreed to a sexual liaison, no women said yes.
The study supports the idea that women are much more selective and engage in inter-sexual selection (carefully picking mates), whereas men are intra-sexual (picked by women).
Sexual Selection Example
The two types of sexual selection strategies described above can be seen in the Andean cock-of-the-rock bird. These birds are found in South America and are very colourful.
Their sexual selection strategy is very well-defined.
- When the female needs to choose a partner to mate with, males take part in communal leks. In a lek, males face one another and perform a confrontational display. Males are not actively fighting but rather are engaging in choreography.
- During the lek, the males face each other and bow, jump and flap their wings. The lek becomes more intense when the female gets closer, and males may even grunt at one another.
This is an example of how intra-sexual selection takes place through two birds competing against one another. The inter-sexual selection strategy involves the female watching how the males engage in the lek.
Fig. 2 - The cock-of-the-rock bird engages in sexual selection.
Relationship between Sexual Selection and Human Reproductive Behaviour
The relationship between sexual selection and human reproduction has been widely explored in psychological literature.
Some of the literature has focussed on physical attractiveness. Physical attractiveness refers to what individuals find physically appealing about the person. Although there are individual differences in physical attractiveness, there is some consensus on what individuals find attractive.
- This is because physical traits that are perceived attractive are usually a sign of fertility and generic fitness.
Singh (1993) studied the preferred waist-to-hip ratio of men as a sign of female fertility. When studying the waist-to-hip ratio of Miss America winners over a decade, they found that men generally find a waist-to-hip ratio of 0.7 attractive (large hips and a slim waist).
Singh argued that men unconsciously take this as a sign that a woman is fertile and healthy, so the attraction is motivated by the evolutionary desire to reproduce.
Waynforth and Dunbar (1995) also conducted a study on attractiveness.
- They reviewed 'Lonely Hearts' columns in American newspapers and found that men advertised their resources and intelligence whilst women described themselves in terms of physical attractiveness and youth.
The study demonstrates how males and females display their traits to potential partners and identify characteristics they deem most desirable to the opposite sex.
Further evidence of the relationship between sexual selection and reproduction comes from Buss' (1995) study in which he explores jealousy in males and females.
- The study's results indicated that women tended to be jealous of emotional intimacy, whereas men feared sexual intimacy. Buss stated that this supports biological explanations of reproductive behaviour as men fear sexual intimacy more due to the possibility of a woman having another man's child.
- On the other hand, women fear emotional intimacy as this puts their security and resources at risk.
Differences between Sexual Selection and Human Reproductive Behaviour
As we discussed above, males and females tend to have different choices when it comes to sexual selection. As a result, this has a direct impact on reproductive behaviour. Sexual selection is the prelude to reproductive behaviour; sexual selection identifies the best candidate to mate with, affecting human reproductive behaviour.
Women will seek strong, independent, high-resource men to secure their futures and increase their chances of survival, and men will seek attractive, youthful women to increase their chances of reproducing. This may affect short-term and long-term partner choices.
Males, for instance, may prefer short-term, casual relationships to increase their chances of securing offspring. Whilst men are most fertile in their younger years, much like women, they continue to be fertile throughout their lives (although their ability to reproduce declines with age), unlike women.
Females' fertility declines more harshly than males, and after menopause, women can no longer conceive children. Females may be more selective in sexual selection choices, as they have a finite amount of time to reproduce.
Sexual selection and reproductive behaviour often link back to times when humans were hunter-gatherers.
Evolutionary psychology suggests desirable traits are indicators of successful genes that increase the chances of survival.
Interestingly, natural selection and sexual selection can conflict. Features deemed attractive can be linked to lower chances of survival. A male bird with bright feathers, whilst is deemed desirable to female birds, it will naturally stand out and attract predators. However, the increased chances of attracting female attention to produce offspring are worth the potential sacrifice.
This is also found in human reproductive behaviour, as certain traits are linked to disadvantages, yet they are deemed attractive.
Evaluation of Sexual Selection
Buss (1989) supports the theory of sexual selection through their study using questionnaires. They gathered data from 10,000 men and women.
- According to the study, due to limited access to resources, women seek men who can provide these resources, and men seek women who are the most fertile, indicated by their levels of physical attractiveness. Women seek resources, and men value reproductive capabilities.
Singh (1993) also supports the theory with their argument regarding waist-to-hip ratio preferences. Singh (2002) linked the waist-to-hip ratio to health and reproductive abilities.
While the evolutionary perspective has provided extensive research on sexual selection, it is not exempt from criticism.
One of the main arguments that have been provided that question the approach is the presence of gender bias. The sexual selection theory suggests that short-term mating is more common in males. However, this would not be a phenomenon if females were unwilling.
Furthermore, Greiling and Buss (2000) found that women can also show a preference for mate-switching because this encourages the diversity of their offspring.
Furthermore, this theory fails to account for major social and cultural changes which may affect reproductive behaviour.
Today women are not dependent on men for survival and men can tell if a child is theirs or not through DNA testing.
This means that women do not have to invest as deeply in finding the perfect mate, and men do not have to spread their seed so widely to be sure they have a child. Therefore, nowadays, mate choice is likely influenced by factors other than just evolutionary preferences.
Buss (1989) also identified more similarities than differences in sexual selection. Resources was not deemed as important as mutual attraction and intelligence.
Sexual Selection - Key takeaways
Sexual selection refers to the evolutionary explanation describing why humans prefer some partners over others. There are two main types of sexual selection strategies: inter-sexual and intra-sexual selection.
Inter-sexual selection refers to the competing nature males use to gain the attention of female partners. Intra-sexual selection refers to when males compete for a female of the same species, and the winner claims the right to mate with the female.
An example of sexual selection is the waist-to-hip ratio preferences in women, where Singh (1993) found that a waist-to-hip ratio of 0.7 was deemed the most attractive due to its links with reproductive abilities and health.
Evidence of the relationship between sexual selection and human productive behaviour comes from research looking into physical attractiveness. Certain characteristics increase the chances of reproducing and securing a mate, known as reproductive advantages.
Sexual selection cannot explain all types of mate choice these days. Social and cultural changes discount the theory, and Buss (1989) found more similarities than differences in their study on differences in mate selection.
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